This application is a 371 of PCT/EP00/02288 filed Mar. 15, 2000, now WO 00/55164.
The present invention relates to phosphabenzene compounds and their use in complexes of transition metals of transition group VIII of the Periodic Table of the Elements in the preparation of aldehydes by hydroformylation of olefins using CO/H2 at up to 200xc2x0 C. and pressures of up to 700 bar.
Hydroformylation is a known process utilized industrially for the preparation of aldehydes from olefins, carbon monoxide and hydrogen. As described in WO 97/46507, phosphabenzenes are active cocatalysts for the hydroformylation of olefins. This document describes a process for preparing aldehydes by hydroformylation of olefins using CO/H2 in the presence of complexes containing phosphabenzene compounds as ligands.
However, the phosphabenzene compounds used, for example 2,4,6-triphenylphosphabenzene and 2,6-bis(2-naphthyl)-4-phenylphosphabenzene, but also phosphabenzenes such as 2,3,5,6-tetraphenylphosphabenzene or 2,3,4,5,6-pentaphenylphosphabenzene, have the disadvantage that they can be degraded under hydroformylation conditions by partial or complete hydrogenation of the phosphabenzene system and subsequent addition reactions (see Examples 11-14). This forms, inter alia, secondary and tertiary phosphines which greatly inhibit the hydroformylation activity of the catalyst system.
Similar phosphabenzene compounds are described in DE-A-19 621 967 and DE-A-16 68 416.
It is an object of the present invention to provide phosphabenzene ligands which avoid the disadvantages of the known ligands.
We have found that this object is achieved by phosphabenzene compounds of the formula (I) 
where the radicals R1 to R13 are, independently of one another, hydrogen, COOM, SO3M, NR3X, NR2, OR, COOR or SR (where M=hydrogen, NH4 or alkali metal, X=anion, R=hydrogen or C1-C6-alkyl), or C1-C12-alkyl, C6-C12-aryl, C7-C12-aralkyl, C7-C12-alkaryl or C3-C6-heteroaromatics, where the alkyl, aryl, alkaryl and aralkyl radicals may bear the abovementioned radicals as substituents and two or more of the radicals may be joined to form aliphatic or fused-on rings, where at least one of the radicals R4 and R8 and at least one of the radicals R9 and R13 is not hydrogen.
Preferably, at least one of the radicals R4 and R8 and at least one of the radicals R9 and R13 are, independently of one another, C1-C12-alkyl, C6-C12-aryl, C7-C12-aralkyl or C7-C12-alkaryl, or R4 and R3 and/or R13 and R1 form a C2-C4-alkylene radical.
Particularly preferably, at least one of the radicals R4 and R8 and at least one of the radicals R9 and R13 are C1-C6-alkyl, or (R4 and R3) and (R13 and R1) in each case form a C2-C3-alkylene radical.
R2 is preferably a phenyl radical which may be substituted by from 1 to 5, preferably from 1 to 3, in particular 1 or 2, C1-C6-alkyl radicals.
Particularly preferably, the radicals R1 and R3 are hydrogen and in each case at most three of the radicals R4 to R8 and R9 to R13 are not hydrogen. The radicals R4 to R8 and R9 to R13 in each case particularly preferably have a maximum of 6, in particular a maximum of 3, carbon atoms. In particular, the phosphobenzene compounds of the formula (I) have no atoms apart from the one phosphorus atom which are not carbon or hydrogen.
The compounds of the formula (I) preferably contain, in addition to the phosphobenzene ring, from 3 to 5, in particular 3, further aromatic rings. The number of alkyl radicals in the compounds of the formula (I) is preferably 0 in the case of purely cyclic structures, otherwise preferably from 2 to 7, in particular from 2 to 6. The alkyl radicals can be linear or branched. Preferably, only linear alkyl radicals are present. The same applies analogously to bridging alkylene groups.
Examples of phosphobenzenes which may be mentioned are: 
It has been found that, in particular, the introduction of 2-alkylaryl substituents in the 2 and 6 positions of the phosphobenzene system gives a significantly increased stability of the cocatalyst under hydroformylation conditions an d the catalyst systems display comparable activities to those of corresponding unsubstituted systems.
The degradation of phosphobenzene compounds having 2-alkylaryl substituents in the 2 and 6 positions of the phosphobenzene system under hydroformylation conditions is significantly reduced compared to analogous systems bearing unsubstituted aryl substituents.
The principle of the preparation of the phosphobenzenes is known. General synthetic methods may be found in G. Mxc3xa4rkl in Multiple Bonds and Low Coordination in Phosphorus Chemistry (Editors M. Regitz, O. J. Scherer), Thieme, Stuttgart, 1990, pp. 220 to 257 (and the references cited therein). Processes for preparing phosphobenzene compounds from pyrylium salts by reaction with phosphine are described in WO 97/46507, DE-A-196 21 967 and the earlier-priority DE-A-197 43 197 which is not a prior publication.
The preparation is preferably carried out by reacting corresponding pyrylium salts with PH3 in the presence or absence of a catalytic amount of acid or base and in the presence or absence of a solvent or diluent. The pyrylium salts are preferably brought into contact with PH3 at above 0xc2x0 C. and reacted at from 0xc2x0 C. to 200xc2x0 C. and a pressure above 1 bar.
It has been found, according to the present invention, that phosphobenzene compounds of the formula above are obtainable by reaction of the corresponding pyrylium salts, i.e. compounds in which the phosphorus in the formula is replaced by O+ together with a corresponding counterion, with PH3 if particular process conditions are adhered to. The pyrylium salts are commercially available or can be prepared by simple means. PH3 is commercially available.
The reaction is preferably carried out at a PH3 partial pressure in the range from 0.1 to 100 bar, particularly preferably from 5 to 35 bar, in particular from 20 to 30 bar. The total pressure in the system depends on the solvent employed. The total pressure can be increased by injection of PH3 or inert gas.
PH3 is preferably passed into the reaction mixture during the reaction in order to keep the PH3 partial pressure essentially constant. This procedure allows a particularly economical and rapid reaction to form the desired phosphobenzene compounds. High product purities and conversions are achieved. The process of the present invention can be used reliably for many products. It can be carried out continuously or batchwise, preferably batchwise. In a particularly advantageous process variant, the pyrylium salts are combined with PH3 at ambient temperature, and the mixture obtained in this way is heated to from 60 to 140xc2x0 C., preferably from 80 to 130xc2x0 C., in order to bring about the reaction.
The reaction temperature is particularly preferably in the range from 100 to 120xc2x0 C. The reaction is preferably carried out in an autoclave. In addition to PH3, it is possible to make additional use of an inert gas by means of which the desired total pressure is set. However, preference is given to using only PH3.
The reaction can be carried out in the presence or absence of a solvent or diluent. It is preferably carried out in the presence of a solvent or diluent. Suitable solvents or diluents are, for example, lower aliphatic alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, tert-butanol or pentanol isomers, preferably ethanol, propanol or butanols, in particular n-butanol.
The reaction can be carried out in the presence of an acid catalyst. Suitable acid catalysts are mineral acids such as HI, HCl, HBr. In particular, hydrogen bromide in acetic acid or acetic anhydride is used as acid catalyst. Preference is given to carrying out the reaction without an acid catalyst.
After the reaction, the reaction mixture is preferably depressurized and, if desired, purged with an inert gas. The gases given off from the reaction mixture are cooled to separate off unreacted PH3 in liquid form and passed through a separator, and the PH3 separated off is reused in the reaction.
In a particularly economical and ecologically acceptable variant of the process, PH3 is passed into a reactor, the reaction is carried out, and the gas stream is passed via a further line through a cooler of any construction type in which the PH3 is condensed out. In a downstream separator of any construction type, the PH3 is then separated off and returned to the reaction, for example by means of a pump. In order to obtain a waste gas which is particularly low in PH3, the use of a second, downstream cooler and separator is advantageous. In order to free the reactor gas space and the equipment used completely of PH3, which is advantageous because of the toxicity of PH3, a flushing line for flushing with an inert gas such as nitrogen should be provided. In this case, the flushing gas should be passed through the combination of cooler and separator.
The time required for the reaction depends on the type of pyrylium salt. Depending on the pyrylium salt, the reaction is preferably carried out for a period of from 1 to 4 hours. The amount of acid catalyst used is, based on the pyrylium salt, preferably from 0.01 to 1%, particularly preferably from 0.03 to 0.1%. In the reaction using a solvent, the concentration of PH3 in the solvent depends on the PH3 partial pressure and on the type of solvent; particularly when carrying out the reaction continuously, a high concentration of PH3 in the solvent should be maintained.
To achieve high conversions in a short reaction time, high PH3 pressures and continuous injection of further PH3 are preferably employed.
Many different pyrylium salts can be used in the process of the invention. The process is generally not restricted to particular classes of compounds. For example, the pyrylium salts can be ferrates, zincates, chlorides, borates, with or without a C1-C16-alkyl radical, triflates, trifluoroacetates or preferably tetrafluoroborates, perchlorates, hydrogen sulfates, bromides, iodides or mixtures thereof. Preference is given to using tetrafluoroborates. The organic group of the pyrylium salts used according to the present invention is described in more detail below by means of the phosphobenzene compounds prepared therefrom.
This process allows the above compounds to be prepared. Compounds which have not yet been described in detail can be obtained analogously.
The activity of phosphobenzene compounds having 2-alkylaryl substituents in the 2 and 6 positions of the phosphobenzene system as cocatalyst in hydroformylation is comparable to analogous systems bearing unsubstituted aryl substituents (see WO 97/02757 and Examples 6, 7, 9 and 10).
The compounds of the present invention can be used for preparing complexes with metals of transition group VIII of the Periodic Table of the Elements. Such complexes can be used as (co)catalysts in hydroformylations of olefins using CO/H2. Suitable reaction conditions are described in DE-A-196 21 967 and WO 97/02757.
The most effective catalysts are those of the formula M(L)n(CO)m in which M is at least one central atom of an element of transition group VIII of the Periodic Table of the Elements, L is at least one ligand of the formula I, n and m are each at least 1 to 3 and the sum n+m is from 2 to 5, and further radicals such as hydrido or alkyl or acyl radicals may be present as ligands.
The active carbonyl complex is generally formed in situ, i.e. in the hydroformylation reactor, from a salt or compound of the metal M, the ligand and carbon monoxide, but it can also be prepared separately and used as such.
The catalyst complexes preferably comprise a central atom M selected from among the transition metals cobalt, ruthenium, rhodium, palladium and platinum, in particular cobalt and rhodium, complexed by carbonyl groups and hydrido, alkyl or acyl radicals and the preferred monodentate or polydentate phosphabenzenes to be used according to the present invention as ligands. If the catalyst complexes are produced in situ, simple precursor complexes such as biscarbonylrhodium acetylacetonate or rhodium acetate are exposed to the reaction conditions En the presence of the corresponding ligands, or precursor complexes are admixed with activating additives such as Bronsted or Lewis acids or Lewis bases.
To form the catalyst in situ in the reaction mixture, the ligand is used in a molar ratio (calculated as equivalents of phosphorus) to rhodium of from 1:1 to 1000:1 and an inert solvent is additionally used. Particularly preferred solvents are the aldehydes which are formed by reaction of the respective olefin, and also the high boilers intrinsic to the synthesis, which are formed by subsequent reactions of the respective aldehyde in the hydroformylation process. In the case of ligands which have been made hydrophilic by means of suitable substituents, preference is given to using water, alcohols or other polar solvents.
The composition of the synthesis gas CO/H2 used in the hydroformylation process of the present invention can be varied within wide limits. For example, synthesis gas having CO/H2 molar ratios of from 5:95 to 70:30 can be successfully used; preference is given to using synthesis gas having CO/H2 ratios of from 40:60 to 60:40, particularly preferably about 1:1.
The hydroformylation reaction with CO and H2 in the presence of the catalyst is carried out at from 0 to 200xc2x0 C., preferably from 20 to 180xc2x0 C., in particular from 50 to 150xc2x0 C. However, an optimum temperature is advantageously determined by experiment for each catalyst system. Depending on the (co)catalyst, i.e. the ligand, and the substrate, the reaction pressure can vary in a range from atmospheric pressure to 700 bar, preferably up to 300 bar. Reactions in a range up to about 30 bar are normally referred to as low-pressure reactions, those in a range up to about 100 bar as intermediate-pressure reactions and those over 100 bar as high-pressure reactions.
In the hydroformylation reaction, the catalyst is generally homogeneously dissolved in the reaction medium and is separated from the reaction product and reused in the hydroformylation stage.
The process generally gives exclusively the corresponding aldehydes in excellent yields.
Olefins which can be hydroformylated according to the present invention are xcex1-olefins or internal olefins or internal, branched olefins. Examples which may be mentioned are the following: ethylene, propene, 1-butene, 1-octene, C5-C20-xcex1-olefins, linear C5-C20 internal olefins, 2-butene; branched, internal octene mixtures; branched, internal nonene mixtures; branched, internal dodecene mixtures, cyclohexene, xcex1-pinene, styrene, 4-isobutylstyrene, methyl 3-pentenoate, methyl 4-pentenoate, methyl oleate, 3-pentenonitrile, 4-pentenonitrile, 2,7-octadien-1-ol, 7-octanal, methyl acrylate, methyl methacrylate, acrylonitrile, vinyl acetate, vinyl glycol diacetate, vinyl methyl ether, polypropene, polyisobutylene. Further suitable substrates are dienes or polyenes having isolated or conjugated double bonds. Examples are 1,3-butadiene, 1,5-hexadiene, vinylcyclohexene, dicyclopentadiene, 1,5,9-cyclooctatriene, butadiene homopolymers and copolymers, polyisobutene.
Otherwise, the hydroformylation reaction is carried out in a manner known per se. Details of the process conditions may be found in Belier et al., Journal of Molecular Catalysis A: 104 (1995) 17-85 and Falbe, Ed., New Syntheses with Carbon Monoxide, Springer, Berlin 1980, p. 55ff.